1. Field of the Invention
The present invention relates to a manufacturing method of a magnetoresistive element for reading a magnetic field intensity of a magnetic recording medium or the like as a signal and a film forming apparatus for carrying out the manufacturing method.
2. Description of the Related Art
With a high density of a hard disk (HDD), there is a demand for a high-sensitivity high-output head. To satisfy the demand, a giant magnetoresistive (GMR) film having a further enhanced property, a ferromagnetic tunnel magnetoresistive (TMR) element utilizing a ferromagnetic tunnel effect, and a current perpendicular to the plane (CPP)-GMR element have newly been proposed.
In order to enhance the property of the GMR film, a method of reducing thickness of a so-called free layer, for example, thickness of a nonmagnetic spacer layer formed, for example, of Cu is basically used. When the layer is thinned in this manner, a resistance value and resistance change amount of the GMR film can be increased. As a result, an output can be increased. Moreover, when recording density is progressively enhanced, the GMR film has to be thin also from a demand for reduction of a shield gap. However, with the thinned layer, there is a problem that ferromagnetic coupling effect (orange peel effect) of so-called pinned and free layers of the GMR film increases and that reproduction sensitivity of the head is dulled. It has been reported that the ferromagnetic coupling is brought about by surface roughness of an interface of the nonmagnetic spacer layer (e.g., Cu layer), and there has been a demand for a technique of smoothening the interface.
Generally in a research of formation of a deposited film, a technique of fining a grain constituting the film is known as one technique for enhancing smoothness of the deposited film, and for this a technique of forming the deposited film while cooling a substrate is known.
Such conventional vapor deposition method performed while cooling the substrate is applied to a sputtering process used simply in a process of forming a magnetoresistive film. It has been found that the following disadvantages occur in this method.
That is, when the substrate is cooled and subsequently the film is sputtered/formed in a vacuum film forming apparatus, a method of forming a structure for passing refrigerants such as liquid nitrogen and liquid helium into a substrate holder, leaving the substrate laid on the holder to stand for a predetermined time to cool the substrate, and successively depositing a predetermined laminated film indicating a magnetoresistive effect on the substrate by a sputtering process is used.
However, since the structure for passing the refrigerant through the substrate holder is used in the method, the substrate cannot be rotated during film formation. Therefore, a state of the thin film deposited on the substrate tends to differ with a substrate position. For example, when 4,000 elements are formed from one wafer substrate, dispersion of properties among the respective elements is possibly generated.
Moreover, when one stage is used to perform a substrate cooling operation and film forming operation in a usual film forming apparatus not particularly devised, the following two problems arise from a viewpoint of productivity. That is, as one problem, a waiting time of about 30 minutes is required from when the substrate is set in the substrate position in a film forming chamber until the substrate is cooled at a desired temperature. During this time, the film forming operation is discontinued. As the other problem, after the film formation, a waiting time is necessary until the substrate temperature returns to room temperature. A reason why the waiting time is necessary to set the substrate temperature back to the room temperature is that dew condensation occurs with the cooled substrate laid in the atmosphere and the film is corroded.
To solve the aforementioned problem, the present inventors have noted properties of a substrate usable in a magnetoresistive element, have intensively researched inventive process steps irrespective of a conventional process technique, and have developed a manufacturing method of a magnetoresistive element which has little dispersion of element properties, high reliability, and superior productivity.
That is, according to the present invention, there is provided a manufacturing method of a magnetoresistive element comprising: a step of preparing a substrate having a thermal conductivity in a range of 5 to 150 Wmxe2x88x921Kxe2x88x921; a substrate cooling step of moving the substrate into a vacuum cooling chamber, and cooling the substrate in the vacuum cooling chamber at an absolute temperature of 200 K or less; and a laminated film forming step of moving the cooled substrate into a vacuum film forming chamber, fixing the substrate to a substrate holder, and forming a magnetoresistive laminated film on the substrate while rotating the substrate.
Moreover, according to the present invention, there is provided a manufacturing method of a magnetoresistive element comprising: a step of preparing a substrate having a thermal conductivity in a range of 5 to 150 Wmxe2x88x921Kxe2x88x921; a substrate cooling step of moving the substrate into a vacuum cooling chamber, and cooling the substrate in the vacuum cooling chamber at an absolute temperature of 200 K or less; a laminated film forming step of moving the cooled substrate into a vacuum film forming chamber, fixing the substrate to a substrate holder, and forming a magnetoresistive laminated film on the substrate while rotating the substrate; and a step of moving the substrate with the laminated film formed thereon into a vacuum temperature raising chamber, and raising the temperature of the substrate with the film formed thereon in a forced manner in the vacuum temperature raising chamber.
Moreover, in a preferred embodiment, the magnetoresistive laminated film in the present invention is constituted as a giant magnetoresistive film.
Furthermore, in another preferred embodiment, the magnetoresistive laminated film in the present invention is constituted as a tunnel magnetoresistive film.
Additionally, in another preferred embodiment, the magnetoresistive laminated film in the present invention is constituted as a spin-valve magnetoresistive film.
Moreover, in another preferred embodiment, the magnetoresistive laminated film in the present invention is constituted as a film formed by a sputtering process.
According to the present invention, there is provided a film forming apparatus comprising: a substrate standby chamber in which a substrate is on standby; a substrate cooling chamber for cooling the substrate; a vacuum film forming chamber for forming a magnetoresistive laminated film on the substrate; and a robot chamber including a robot which can convey the substrate at least to the substrate standby chamber, the substrate cooling chamber and the vacuum film forming chamber, wherein the substrate standby chamber, the substrate cooling chamber and the vacuum film forming chamber are disposed as independent chambers centering on and on a peripheral edge of the robot chamber via respective shutters.
According to the present invention, there is provided a film forming apparatus comprising: a substrate standby chamber in which a substrate is on standby; a substrate cooling chamber for cooling the substrate; a vacuum film forming chamber for forming a magnetoresistive laminated film on the substrate; a vacuum temperature raising chamber for raising a temperature of the substrate with the magnetoresistive laminated film formed thereon in a forced manner; and a robot chamber including a robot which can convey the substrate at least to the substrate standby chamber, the substrate cooling chamber, the vacuum film forming chamber, and the vacuum temperature raising chamber, wherein the substrate standby chamber, the substrate cooling chamber, the vacuum film forming chamber, and the vacuum temperature raising chamber are disposed as independent chambers centering on and on a peripheral edge of the robot chamber via respective shutters.